Polymorphic forms of perindopril (L)-arginine and process for the preparation thereof

ABSTRACT

The present invention relates to novel and stable polymorphic forms of Perindopril (L)-Arginine designated as Form γ and amorphous form and processes for their preparation. The present invention also provides the novel polymorph Form γ with greater stability to heat and humidity and can be prepared on large scale by an efficient, economic and reproducible process.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a national phase entry under 35 U.S.C. §371of International Application No. PCT/IN2009/000357, filed Jun. 22, 2009,published in English, which claims the benefit of Indian patentapplication No. 1535/CHE/2008 filed on Jun. 24, 2008, the disclosures ofsaid applications are incorporated by reference herein.

FIELD OF THE INVENTION

The present invention provides novel polymorphic form gamma (γ) ofPerindopril (L)-Arginine and amorphous form of Perindopril (L)-Arginine.The present invention also provides novel processes for the preparationof polymorphic form gamma (γ) of Perindopril (L)-Arginine and theamorphous form of Perindopril (L)-Arginine.

BACKGROUND OF THE INVENTION

Angiotensin-converting enzyme (ACE) inhibitors are used to treat highblood pressure and some types of heart failure. Perindopril,(2S)-2-[(1S)-1-carbethoxybutylamino]-1-oxopropyl-(2S,3aS,7aS)-perhydroindole-2-carboxylicacid of formula (I), is a potential (ACE) inhibitor. Perindoprilerbumine salt is marketed under the brandname ACEON®.

U.S. Pat. No. 4,508,729 and EP 004965881 patents have disclosedPerindopril and its pharmaceutically acceptable salts, whereinpharmaceutically acceptable salt is selected from the group comprisingmineral organic, base or acid such as the sodium salt or maleate salt.This patent also disclosed the stability of maleate and sodium salts ofPerindopril. In the course of stability studies towards temperature andhumidity, it is found that sodium salt is not suitable for making theformulation because it is immediately converted into oil on contact withthe atmosphere. With respect to the maleate salt, it degrades rapidlyunder such conditions (approximately 25 to 30% of product degraded in 8days at 50° C.).

U.S. Pat. No. 4,914,214 discloses a process for the preparation ofPerindopril and its tert-butylamine salt (Perindopril erbumine). Thetert-butylamine salt has exhibited the best stability compared to theother salts studied till then. But, in view of the intrinsic fragilityof Perindopril, the tert-butylamine salt has not been capable ofproviding a complete solution to the problems of the product's stabilitytowards heat and humidity. Indeed, for marketing tablets of Perindopriltert-butylamine salt in certain countries, additional packaging is foundto be essential. Moreover, even for temperate-climate countries, theinstability of the product has made it impossible to obtain a shelf-lifeof more than 2 years for the tablets. Finally, for marketing thetablets, they have to be marked “to be stored at a temperature less thanor equal to 30 degrees”.

According to the prior art, Perindopril, tert-butylamine salt is storedin a special package and requires appropriate storage conditions, thusmaking it a costly issue. Thus, there is a need to develop a new salt,which is having good stability in different temperatures and humidityconditions.

Numerous salts were studied and, as indicated hereinbefore, the saltscustomarily used in the pharmaceutical sector proved to be unstable. Onthe other hand, and in surprising manner, it has been found that theArginine salt of Perindopril, besides being new, has many unexpectedadvantages over all the other salts studied so far, especially, over thetert-butylamine salt of Perindopril.

Perindopril Arginine represented by the formula (II), its hydrates,pharmaceutical composition and a method of treatment is first disclosedin U.S. Pat. No. 6,696,481. This patent also disclosed that the Argininesalt of Perindopril is an alternate to tert-butylamine salt havingsuperior properties in terms of stability towards heat and humidity.

US '481 patent does not disclose the experimental details forpreparation of the hydrates of Arginine salt of Perindopril. The saidhydrates are not characterized by moisture content, DSC and PXRDpattern. In addition to this, the said patent claims Arginine salt ofPerindopril and hydrates thereof.

WO 2007099216 claims beta (β) crystalline polymorphic form of(L)-Arginine salt of Perindopril and process for the preparationthereof.

WO 2007099217 claims alpha (α) crystalline form of the (L)-Arginine saltof Perindopril and process for the preparation thereof.

WO '216 and WO '217 patent applications provided 2θ, d-spacing valuesand intensity table for Form α and Form β but no PXRD pattern isdisclosed. These applications further provides insufficient experimentaldetails in each case by disclosing only a single example (example-1) forpreparation of Form α and Form β.

According to WO '217 English translation, in Example 1, crystalline Formα is prepared by dissolving 1:1 molar ratio of Perindopril and(L)-Arginine in water at ambient temperature under stirring, followed byaddition of methylcyclohexane and then dimethylsulfoxide. The solutionis cooled to 20° C. and maintained under stirring. The solid obtained isfiltered, washed and dried. The reproduction of Example 1 of WO'217 inour laboratories afforded Form α inconsistently (success rate 10%) withcharacteristic peaks as disclosed in WO '217 application (FIG. 3). Wefurther simulated the PXRD pattern of Form α from the literature data(WO '217 PXRD table) which is similar to our experimental PXRD pattern(FIG. 4). The water content of the experimental Form α is in the rangeof 3-4% which further confirms that the form α is a hydrate, preferablymonohydrate.

According to WO '216 English translation, Example 1, crystalline Form βis prepared by dissolving the salt of (L)-Arginine of Perindopril inacetonitrile at reflux temperature. After 1 hour stirring under reflux,the crystals obtained are filtered at a temperature of 80° C. Thecrystals obtained are dried, which leads to Form β in anhydrous form.However, the reproduction of Example 1 of WO'216 in our laboratoriesnever obtained Form β. Also we attempted several other processvariations for the preparation of Form β such as starting from 1:1 molarratios of Perindopril and (L)-Arginine or from Perindopril (L)-Argininesalt using different solvent combinations at different temperatures butwe failed to reproduce Form β.

According to WO '216 crystalline form β is an anhydrous form whichprompted us to look at several other processes techniques to removemoisture from Form α (monohydrate) such as azeotropic distillationand/or by drying. But even after reducing the moisture content below 1%(Table-2) we failed to obtain Form β. From this it appears that WO'216application process is not suitable for the preparation of form β orpolymorphic form β in an elusive form.

In view of the above prior problems, there is an unmet need for a stableform of Perindopril (L)-Arginine which can be prepared by an efficient,economic and reproducible process, particularly to large scalepreparation. Further it should be suitable for handling and haveexcellent physical and chemical stability towards heat and humidity atdifferent conditions.

Amorphous forms of an API are characterized by decreasing amounts oflong range order in the solid state and may enjoy enhanced propertieswith respect to crystalline forms of the solid. Also relevant is thedegree of amorphous character. Crystallinity and amorphicity arecontinuous properties and a particular solid may have a degree ofcrystallinity that ranges from 0% (fully amorphous) to 100% (fullycrystalline). The structural basis for losses in crystallinity couldarise from progressive “decrystallization” throughout the solid orthrough a growth of amorphous regions within the crystalline matrix(Polymorphism: in the Pharmaceutical Industry, R. Hilfiker (Ed.),Wiley-VCH, Weinheim, Chapter 10, pp. 259-285, 2006). It is noted that noamorphous forms of Perindopril (L)-Arginine are satisfactorilycharacterized.

OBJECTIVE OF THE INVENTION

The main object of the present invention is to provide novel polymorphicform gamma (γ) of Perindopril (L)-Arginine.

Another object of the present invention is to provide Perindopril(L)-Arginine (γ) form having the degree of crystallinity under 60%.

Yet another object of the present invention is to provide novel processfor the preparation of novel polymorphic form gamma (γ) of Perindopril(L)-Arginine.

Yet another object of the present invention is to provide athermodynamically more stable polymorphic form γ of Perindopril(L)-Arginine which has enhanced physical and chemical stability towardsheat and humidity, than prior art.

The main object of the present invention is to provide novel amorphousform of Perindopril (L)-Arginine.

Another object of the present invention is to provide novel process forthe preparation of amorphous Perindopril (L)-Arginine.

SUMMARY OF THE INVENTION

In one aspect of the present invention relates to novel and stablepolymorphic form of Perindopril (L)-Arginine salt designated as Formgamma (γ).

In another aspect, the present invention relates to novel polymorphicform γ of Perindopril (L)-Arginine, characterized by a powder X-raydiffraction pattern and shown in FIG. 1.

In yet another aspect, the present invention relates to novelpolymorphic form γ of Perindopril (L)-Arginine, characterized by apowder X-ray diffraction pattern with peaks at about 4.21, 7.87, 13.19,14.12, 17.60, 20.15±0.2 degrees 2-Theta.

In yet another aspect of the present invention is to provide Perindopril(L)-Arginine (γ) form having the degree of crystallinity under 60%.

In yet another object of the present invention is to provide athermodynamically more stable polymorphic form gamma (γ) of Perindopril(L)-Arginine which has enhanced physical and chemical stability towardsheat and humidity, when compared to the prior art.

In yet another object of the present invention is to provide a novelprocess for the preparation of novel polymorphic form gamma (γ) ofPerindopril (L)-Arginine.

In another aspect, the present invention relates to a novel process forthe preparation of the polymorphic Form γ of Perindopril (L)-Argininecomprising the steps of a) dissolving Perindopril in water or suitableorganic solvent b) adding (L)-Arginine c) removing the solvent and d)isolating novel polymorphic form γ of Perindopril (L)-Arginine.

In yet another aspect, the present invention relates to a novel processfor the preparation of polymorphic form γ of Perindopril (L)-Argininecomprising the steps of a) dissolving Perindopril (L)-Arginine insuitable organic solvent b) adding suitable antisolvent and c) isolatingnovel polymorphic form γ of Perindopril (L)-Arginine.

In yet another aspect, the present invention relates to a novel processfor the preparation of polymorphic form γ of Perindopril (L)-Argininecomprising the steps of a) suspending Perindopril free acid and Argininein suitable organic solvent at room temperature b) heating the reactionmixture to reflux temperature followed by azeotropic distillation c)adding suitable antisolvent and d) isolating novel polymorphic form γ ofPerindopril (L)-Arginine.

In yet another aspect, the present invention relates to a novel processfor the preparation of polymorphic form γ of Perindopril (L)-Argininecomprising the steps of a) suspending Perindopril free acid and Argininein suitable organic solvent b) heating the reaction mass to refluxtemperature to get clear solution c) cooling the reaction mass d) addingsuitable antisolvent and e) isolating novel polymorphic form γ ofPerindopril (L)-Arginine.

In yet another aspect, the present invention relates to a novel processfor the preparation of polymorphic form γ of Perindopril (L)-Argininecomprising the steps of a) dissolving perindopril free acid and argininein water at ambient temperature b) adding the first solvent c) coolingthe resulting solution of step b) then addition of second solvent and d)isolating novel polymorphic form γ of Perindopril (L)-Arginine.

In yet another aspect, the present invention relates to a novel processfor the preparation of polymorphic form γ of Perindopril (L)-Argininecomprising the steps of a) dissolving perindopril free acid in suitableorganic solvent or mixture of organic solvent b) adding argininesolution by dissolving arginine in water and c) isolating novelpolymorphic form γ of Perindopril (L)-Arginine.

In yet another aspect, the present invention relates to a novel processfor the preparation of polymorphic form γ of Perindopril (L)-Argininecomprising the steps of a) suspending perindopril arginine inappropriate solvents b) stirring the resulting slurry of step a) atdifferent temperature and c) isolating novel polymorphic form γ ofPerindopril (L)-Arginine.

In yet another aspect, the present invention relates to a novel processfor the preparation of polymorphic form γ of Perindopril (L)-Arginine byexposing amorphous or α form of Perindopril (L)-Arginine salt to arelative humidity (RH) more than 90% for several hours (table-2),indicating that α form and amorphous form of Perindopril (L)-Arginineare metastable.

In yet another aspect, the present invention relates to hygroscopicstability of the novel polymorphic form γ of Perindopril (L)-Arginine.The hygroscopic studies shows that there is no substantial increase inmoisture content for Form γ when stored in different relative humiditiesfor a period of 1 to 3 months suggesting that Form γ is stable tohumidity.

In yet another aspect, the present invention relates to the conversionof metastable polymorphs of Perindopril (L)-Arginine such as the fullyamorphous form and the α form into the stable polymorphic form γ ofPerindopril (L)-Arginine. The process comprises the steps of suspendingthe fully amorphous form or the α form of Perindopril (L)-Arginine saltin a solvent or mixture of solvents and stirring at room temperature forseveral hours, and then isolating the polymorphic form γ of Perindopril(L)-Arginine.

In yet another aspect, the present invention relates to stability,solubility and storage profile of the novel polymorphic form γ ofPerindopril (L)-Arginine.

In yet another aspect the present invention relates to amorphous form ofPerindopril (L)-Arginine salt.

In yet another aspect, the present invention relates to amorphous formof Perindopril (L)-Arginine characterized by a powder X-ray diffractionpattern, shown in FIG. 2.

In yet another aspect, amorphous form of Perindopril (L)-Arginine saltis further characterized by a glass transition temperature (Tg) at95.84° C. in DSC, shown in FIG. 3.

In yet another aspect, the present invention relates to novel processfor the preparation of amorphous form of Perindopril (L)-Arginine saltcomprising the steps of a) dissolving Perindopril (L)-Arginine salt in asuitable organic solvent b) removing the solvent and c) isolatingamorphous form of Perindopril (L)-Arginine salt.

In yet another aspect, the present invention relates to novel processfor the preparation of amorphous form of Perindopril (L)-Arginine saltcomprising the steps of a) suspending Perindopril in a solvent ormixture of solvents b) heating the reaction mass temperature to refluxfollowed by cooling room temperature c) removing the solvent and d)isolating amorphous form of Perindopril (L)-Arginine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is powder X-ray diffraction diagram of Form γ of Perindopril(L)-Arginine.

FIG. 2 is powder X-ray diffraction diagram of amorphous Perindopril(L)-Arginine.

FIG. 3 is modulated DSC thermogram of amorphous Perindopril(L)-Arginine.

FIG. 4 is powder X-ray diffraction diagram of Perindopril (L)-ArginineForm α (as per example 1 of WO'217).

FIG. 5 is the overlay of experimental and simulated Powder X-raydiffraction diagram of Perindopril (L)-Arginine Form α

FIG. 6 is SEM images of A) Form α, B) Amorphous and C) Form γ ofPerindopril (L)-Arginine salt.

POWDER X-RAY DIFFRACTION (PXRD)

The PXRD measurements were carried out using PANalytical, X'Pert PROpowder diffractometer equipped with goniometer of θ/θ configuration andX'Celerator detector. The Cu-anode X-ray tube is operated at 40 kV and30 mA. The experiments were conducted over the 2θ range of 2.0°-50.0°,0.030° step size and 50 seconds step time.

Karl-Fisher

Water content was determined on Metrohm Karl-Fisher titrator (Model: 794Basic Titrino) using pyridine free single solution (Merck, Mumbai) withsample mass between 450 mg to 550 mg.

DSC Glass Transition

The glass transition temperature (Tg) of the amorphous Perindopril(L)-Arginine was measured on TA Q1000 of TA instruments with modulatedDSC software. The sample were heated from 40 to 180° C. at heating rateof 5.0° C./min with modulation amplitude ±0.5° C., the modulation period80 sec and nitrogen purging at a flow rate of 50 ml/min. Standardaluminum pans covered by lids with five pin holes were used.

Polarising Light Microscopy (PLM)

Polarising Light Microscopy (DFC-280, Mikroscope Leica DMEP, Germany)was used to determine whether the samples contained birefringence. Theywere examined using a 40-fold magnification.

Scanning Electron Microscopy (SEM)

The samples were mounted onto a strip of double-sided carbon tape andsputter coated with a thin layer of platinum under vacuum prior toanalysis. SEM was performed on JEOL, JSM 6380 instrument using a 2 kVbeam acceleration voltage.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a novel polymorphic form of Perindopril(L)-Arginine salt designated as Form gamma (γ). The present inventionalso relates to a novel fully amorphous form of Perindopril (L)-Argininesalt. The invention further relates to novel processes for thepreparation of novel polymorphic form γ and the fully amorphous form ofPerindopril (L)-Arginine salt. The present invention also providesPerindopril (L)-Arginine (γ) form having a degree of crystallinity under60% with enhanced stability with respect to heat and humidity.

The said forms are differ from each other in their physical properties,and spectral data and method of preparation and are characterized bytheir Powder X-ray Diffraction patterns, differential scanningcalorimetry (DSC), polarizing microscopy (PLM), scanning electronmicroscopy (SEM) and/or by Karl-Fisher (KF) method.

In one embodiment, the present invention provides a novel polymorphicform γ of Perindopril (L)-Arginine, characterized by a powder X-raydiffraction pattern with peaks at about 4.21, 7.87, 13.19, 14.12, 17.60,20.15±0.2 degrees 2-theta, shown in FIG. 1.

The present invention is to provide Perindopril (L)-Arginine (γ) formhaving the degree of crystallinity under 60%, which has enhancedstability to heat and humidity. According to the present invention, theobtained Perindopril (L)-Arginine (γ) form is subjected to acceleratedstability at 40° C. and relative humidity (RH) 75%. The polymorphic formγ of Perindopril (L)-Arginine is found to be chemically and physicallyvery stable. There is no substantial increase in the moisture contentthat is observed. The PXRD pattern remains the same as initially and nodegradation is observed in HPLC.

According to the present invention, there is provided a novel processfor the preparation of novel polymorphic form γ of Perindopril(L)-Arginine comprising the steps of a) dissolving perindopril free acidin water b) adding (L)-Arginine c) removing the solvent and d) isolatingnovel polymorphic form γ of Perindopril (L)-Arginine.

In one of the embodiments of the present invention, Perindopril freeacid is dissolved in water to get clear solution at room temperature.(L)-Arginine is added to the solution and it is maintained for 15 to 30minutes at room temperature. The solvent is removed by using techniquessuch as vacuum distillation, freeze drying and spray drying to obtainthe polymorphic form γ of Perindopril (L)-Arginine.

According to the present invention, there is provided a novel processfor the preparation of the novel polymorphic form γ of Perindopril(L)-Arginine comprising the steps of a) dissolving Perindopril(L)-Arginine in suitable organic solvent at room temperature b) addingsuitable antisolvent and c) isolating novel polymorphic form γ ofPerindopril (L)-Arginine.

In one of the embodiments of the present invention, Perindopril(L)-Arginine is dissolved in a solvent selected from alcohol such asmethanol, ether solvent such as 1,4-dioxane, polar solvents such aspyridine, N-methylpyrrolidone at room temperature. Antisolvent is addedto the above clear solution at room temperature followed by stirring toobtain the polymorphic form γ of Perindopril (L)-Arginine. Anti-solventused for the precipitation is selected from ester solvent such as ethylacetate, ketone solvent such as acetone, ether solvent such as isopropylether or mixtures thereof;

According to the present invention, there is provided a novel processfor the preparation of novel polymorphic form γ of Perindopril(L)-Arginine comprising the steps of a) suspending Perindopril and(L)-Arginine in suitable organic solvent at room temperature b) heatingthe reaction mass to reflux temperature followed by azeotropicdistillation c) adding suitable antisolvent d) isolating novelpolymorphic form γ of Perindopril (L)-Arginine.

In one of the embodiments of the present invention, Perindopril(L)-Arginine is suspended in a suitable organic solvent selected fromaromatic hydrocarbons such as toluene, tetrahydrofuran, dichloroform,dichloroethane or mixtures thereof. The resulting slurry is heated toreflux temperature (70 to 115° C.) to remove the water by azeotropicdistillation. The antisolvent is added at reflux temperature, followedby cooling of the resulting solution to room temperature. Theantisolvent used is selected from ethyl acetate or acetonitrile ormixtures thereof.

According to the present invention, there is provided a novel processfor the preparation of novel polymorphic form γ of Perindopril(L)-Arginine comprising the steps of a) suspending Perindopril free acidand Arginine in suitable organic solvent b) heating the reaction mass toreflux temperature to get clear solution c) cooling the reaction mass d)adding suitable antisolvent and e) isolating novel polymorphic form γ ofPerindopril (L)-Arginine.

In one of the embodiments of the present invention, Perindopril freeacid and Arginine is suspended in a suitable organic solvent selectedfrom alcohol such as methanol. The resulting slurry is heated to refluxtemperature (50 to 70° C.) to give clear solution, which is cooled to 0to 10° C. Antisolvent used for the precipitation is selected from ethersuch as t-butyl methyl ether, diisopropyl ether, diethyl ether ormixtures thereof.

According to the present invention, there is provided a novel processfor the preparation of novel polymorphic form γ of Perindopril(L)-Arginine comprising the steps of a) dissolving Perindopril free acidand (L)-Arginine in water at ambient temperature b) adding the firstsolvent c) cooling the resulting solution of step b) then addition ofsecond solvent and d) isolating novel polymorphic form γ of Perindopril(L)-Arginine.

In one of the embodiments of the present invention, Perindopril freeacid and (L)-Arginine is dissolved in water at temperature 20 to 35° C.to get clear solution. First solvent is added at same temperature and isselected from aliphatic hydrocarbon such as cyclohexane, hexane,aromatic hydrocarbon such a toluene or mixtures thereof. The resultingmixture is cooled to 10 to 20° C.; second solvent is added at 10 to 20°C. The second solvent is selected from a polar solvent such asN-methylpyrrolidone, polar aprotic solvent is N,N-dimethyl formamide,N,N-dimethylacetamide or mixtures thereof.

According to the present invention, there is provided a novel processfor the preparation of novel polymorphic form γ of Perindopril(L)-Arginine comprising the steps of a) dissolving Perindopril free acidin suitable organic solvent b) adding (L)-Arginine solution bydissolving (L)-Arginine in water and c) isolating novel polymorphic formγ of Perindopril (L)-Arginine.

In one of the embodiments of the present invention, Perindopril acid isdissolved in suitable solvent is selected from mixture of water andorganic solvent. The organic solvent is selected from alcohol such asethanol, ketone such as acetone, ether such as 1,4-dioxane. (L)-Arginineis dissolved in water to get solution is added to the above solutionfollowed by stirring and filtration to give polymorphic form γ ofPerindopril (L)-Arginine.

According to the present invention, there is provided a novel processfor the preparation of novel polymorphic form γ of Perindopril(L)-Arginine comprising the steps of a) suspending perindopril argininein suitable solvents b) stirring the resulting slurry of step a) atdifferent temperature and c) isolating novel polymorphic form γ ofPerindopril (L)-Arginine.

In one of the embodiment of the present invention, Perindopril(L)-Arginine is selected from Perindopril (L)-Arginine polymorphic formalpha (α), Perindopril (L)-Arginine polymorphic form γ or Perindopril(L)-Arginine amorphous form. Perindopril Arginine is suspended in asolvent selected from aliphatic hydrocarbons such as n-heptane, aromatichydrocarbon such as toluene, nitrile such as acetonitrile or mixturesthereof. The resulting slurry is stirred at temperature 20 to 115° C.followed by filtration to give polymorphic form γ of Perindopril(L)-Arginine.

According to the present invention, there is provided a novel processfor the preparation of polymorphic form γ of Perindopril (L)-Arginineform by exposing form α or amorphous form of Perindopril (L)-Arginine toa relative humidity (RH>90%) for several hours indicating that α formand amorphous form of Perindopril (L)-Arginine are metastable.

According to the present invention, there is provided a hygroscopicstability of the novel polymorphic form γ of Perindopril (L)-Arginine.The hygroscopic studies shows that there is no substantial increase inmoisture content for Form γ when stored in different relative humiditiesfor a period of 1 to 3 months suggesting that Form γ is stable tohumidity.

In yet another embodiment, the present invention relates to stability,solubility and storage profile of the novel polymorphic form γ ofPerindopril (L) Arginine as defined herein briefly.

According to the present invention, there is provided an amorphous formof Perindopril (L)-Arginine salt.

According to the present invention, there is provided an amorphous formof Perindopril (L)-Arginine having a PXRD pattern as shown in FIG. 2.The amorphous form of Perindopril (L)-Arginine salt is furthercharacterized by a glass transition temperature (Tg) at 95.84° C. inMDSC, shown in FIG. 3.

According to the present invention, there is provided a novel processfor the preparation of amorphous form of Perindopril (L)-Arginine saltcomprising the steps of a) dissolving polymorphic γ form of Perindopril(L)-Arginine in a suitable organic solvent b) removing the solvent bydistillation c) isolating amorphous form of Perindopril (L)-Arginine.

In one embodiment of the present invention, Perindopril (L)-Argininepolymorphic form (γ) is dissolved in solvent selected from alcohol suchas methanol to get the clear solution. The solvent is removed bydistillation with or with out reducing pressure to give amorphous formof Perindopril (L)-Arginine.

According to the present invention, there is provided a novel processfor the preparation of amorphous form of Perindopril (L)-Arginine saltcomprising the steps of a) suspending Perindopril (L)-Arginine in asolvent or mixture of solvents b) heating the reaction mass to refluxtemperature followed by cooling to room temperature c) removing thesolvent and d) isolating amorphous form of Perindopril (L)-Arginine.

In one embodiment of the present invention, Perindopril (L)-Arginine issuspended in a solvent or mixture of solvent selected from alcohols suchas methanol, ethanol, chlorinated solvents such as dichloromethane,dichloroethene or mixture of solvents with water. The resulting slurryis heated to reflux temperature to get clear solution, which is cooledto room temperature. Solvent is removed by distillation or spray dryingto give the fully amorphous form of Perindopril (L)-Arginine.

Solid State Stability

The solid state stability of the novel polymorphic form γ of Perindopril(L)-Arginine was determined by storing approximately 3.0 g of the sampleat accelerated stress conditions (40° C./75% relative humidity) for 15days, 1 month and 2 months. The samples were tested by PXRD, Karl-Fishertitrator and HPLC for final purity and degradation products. The resultsare given in the following Table 1.

TABLE 1 m/c Purity Conditions PXRD (%) (%) Initial Form γ 3.8 99.1 After15 days Same as initial 4.2 99.2 After 1 month Same as initial 4.4 99.2After 2 months Same as initial 5.0 99.1

The polymorphic form γ of Perindopril (L)-Arginine was found to bechemically and physically very stable. There is no substantial increasein moisture content was observed. The PXRD pattern remains same asinitial and there is no degradation observed in HPLC.

Physical Stability

The physical stability of the amorphous form, Form γ and literature Formα of Perindopril (L)-Arginine was determined by storing approximately3.0 g of the sample a) at 50° C., b) at 70° C., c) at 100° C. and d) at90% Relative Humidity (RH). The samples are tested by PXRD andKarl-Fisher titrator after 15 hours and 72 hours. There is no change inform observed in Form γ under both drying and humid conditions butliterature Form α and amorphous form are converted to Form γ inhumidity. The results are shown in the following Table 2.

TABLE 2 Conditions Input Period Results Drying Form α at 70° C. 3 daysForm α Form α at 100° C. 7 days Form γ at 70° C. 3 days Form γ Form γ at100° C. 7 days Amorphous at 25° C. 3 hrs Form γ Humidity Form α 15 hrsForm γ (RH > 90%) Form γ 15 hrs Amorphous 3 hrs

Transformation Kinetics

Solvent-mediated polymorph transformations are an effective method tomeasure the physical stability for both metastable and thermodynamicallystable polymorphs [1]. This study is carried out by slurring 1 g of Formγ, amorphous and literature Form α of Perindopril (L)-Arginine salt indifferent solvents at 25 to 30° C. for several hours. The solid samplesare then characterized by PXRD (example 10, Table 6). No discernibleform conversion or dissociation was observed in heptane for polymorphsForm α and Form γ but form α and amorphous form are converted to form γwhile stirred in toluene or acetonitrile for more than 15 hrs at roomtemperature (Example 10, Table 6).

The above mentioned observations indicate that the novel polymorphicform γ of Perindopril (L)-Arginine is thermodynamically more stable thanPerindopril (L)-Arginine amorphous and form α.

Crystallinity Index

The Crystallinity index is measured quantitatively from the X-ray powderdiffractogram by comparing the area of the crystalline peaks (AC) to thearea under the halo-shaped amorphous peak. Thus (AC+AA) equals the totalscattered intensity. The Crystallinity is representing by the formula:CI=AC*100/(AC+AA). CI is estimated considering the error of ±5%, due tofluctuation in the baseline. We measured the CI of the novel Form γprepared using different methods. The results are shown in below Table3.

TABLE 3 S. No. Method Polymorph Crystallinity Index (%) 1 Freeze dryingForm γ 14 15 15 2 Anti solvent 13 15 26 45

From above table it was observed that the crystallinity of Form γ is inthe range of 10 to 60%, preferably between 10 to 45%.

Polarizing Light Microscopy (PLM)

PLM is very effective tool and can be utilized to differentiate betweenamorphous and crystalline substances. Generally the effects ofbirefringence are observed only in crystalline systems and even smallamount of crystallinity can be detected by PLM.

The three different polymorphs of Perindopril (L)-Arginine salt,literature Form α and novel Form γ and amorphous form are analyzed byPLM. Form γ showed small areas of birefringence which indicate that Formγ may exist in a substantially amorphous state with residualcrystallinity. This is also supported by the crystallinity index (CI)data from PXRD analysis.

Scanning Electron Microscopy (SEM)

SEM was used to obtain more information about the surface and themorphology of three different polymorphs of Perindopril (L)-Argininesalt (FIG. 6). Form α samples showed irregular granular type particleswith rough surface. Amorphous form showed particles of different sizeswith a smooth surface, more in line with the expected appearance ofamorphous organic particles. Form γ has similar particle nature asamorphous however in some regions small agglomerates were observed onthe smooth surface. This further hints Form γ may exist in asubstantially amorphous state with traces of residual crystallinity.

Thermal Analysis

Perindopril (L)-Arginine salt Form α and Form γ have very broad meltingwhich is in the range of 128-136° C. It was very difficult todistinguish these two forms by their melting point. Amorphous form ofPerindopril (L)-Arginine salt has been studied by modulated temperaturedifferential scanning calorimetry (MDSC) for determination of its glasstransition temperature (Tg). The MTDSC experiment was carried out toseparate the reversing glass transition and non-reversing relaxationendotherm. The MDSC response of amorphous form of Perindopril(L)-Arginine salt shows reversible heat flow as shown in FIG. 2 withglass transition temperature (Tg) at 95.84° C.

The following non-limiting examples illustrate specific embodiments ofthe present invention. They are not intended to be limiting the scope ofpresent invention in any way.

Experimental Section Example 1 Process for the Preparation of AmorphousPerindopril (L)-Arginine

15 g of form γ of Perindopril (L)-Arginine was dissolved in methanol(100 ml) at room temperature. The solution was filtered through hyflowbed to remove the undissolved particulates. The resulting solution wasdistilled out completely under vacuum at 50° C. till it was free powder.The solid obtained was identified as amorphous Perindopril Arginine.

Example 2 Preparation of Amorphous Perindopril (L)-Arginine

15 g of Perindopril was suspended in methanol (105 ml) at roomtemperature. To this solution (L)-Arginine (7.1 g) was added and heatedto reflux to get clear solution. The resulting solution was filteredthrough hyflow bed to remove any undissolved particulate. The filtratewas cooled to room temperature and subjected to spray drying to giveamorphous Perindopril (L)-Arginine.

Example 3 Preparation of Amorphous Perindopril (L)-Arginine

10 g of Perindopril was suspended in a 1:1 mixture of methanol and water(5; 5 v/v) of dichloromethane (250 ml) at room temperature. To thissolution (L)-Arginine (7.1 g) was added and heated to reflux to getclear solution. The resulting solution was filtered through hyflow bedto remove any undissolved particulate. The filtrate is then cooled toroom temperature and subjected to spray drying to give amorphousPerindopril (L)-Arginine.

Example 4 Process for the Preparation of Polymorphic Form γ ofPerindopril (L)-Arginine

10 g of Perindopril free acid was dissolved in water (100 ml) and added(L)-Arginine (4.7 g) and stirred for 15 minutes to get clear solution.The resulting solution was filtered through hyflow bed to remove theundissolved particulate. The resulting clear solution was subjected tofreeze drying. The solid obtained is identified as form γ of Perindopril(L)-Arginine.

Example 5 Process for the preparation of polymorphic form γ ofPerindopril (L)-Arginine

10 g of Perindopril free acid was dissolved in water (100 ml) at roomtemperature. To this solution (L)-Arginine (4.7 g) was added and theresulting solution was subjected to spray drying using Buchi mini-spraydryer, (Model: B-290). The solid obtained was identified as form γ ofPerindopril (L)-Arginine.

Example 6 Process for the Preparation of Polymorphic Form γ ofPerindopril (L)-Arginine

5 g of Perindopril free acid and (L)-Arginine (2.3 g) were suspended intoluene (25 ml) at room temperature. The reaction mass was then refluxazeotropically for 60 minutes to get the clear solution. To this clearsolution acetonitrile (250 ml) was added and stirred for 60 minutes at75 to 80° C. The resulting solid was filtered and washed withacetonitrile (20 ml). The product obtained was identified as form γ ofPerindopril (L)-Arginine.

Example 7 Process for the Preparation of Polymorphic Form γ ofPerindopril (L)-Arginine

5 g of Perindopril free acid and (L)-Arginine (2.3 g) is suspended inmethanol (50 ml) at room temperature. The reaction mass was thenrefluxed to get the clear solution and stirred for 60 minutes at 60 to70° C. The resulting solution was cooled to room temperature and thencooled to 0 to 5° C. To this solution IPE (1.0 lit) was added and thenmaintained for 1 hour at 0 to 5° C. The solid obtained is dried for 15hours under vacuum at 50° C.

Example 8 Process for the Preparation of Polymorphic Form γ ofPerindopril (L)-Arginine

2 g of pure Perindopril free acid and (L)-Arginine (0.9 g) are dissolvedin 10 ml of water at 25 to 30° C. To this clear solution indicatedsolvents at the indicated volumes was added at 25 to 30° C. and stirredfor 30 minutes. The resulting solution was cooled to 15 to 20° C. and anindicated anti solvent at the indicated volumes are added slowly. Theresulting reaction mass was stirred for 1 hour at 15 to 20° C. The solidwas filtered and washed with 5 ml of indicated solvents. The wet solidwas dried at 50 to 55° C. under vacuum for 12 hours. The results areshown in following table 4

TABLE 4 Process Input Solvents Result Antisolvent Perindopril + CyH/DMFForm γ (L)-Arginine + CyH/NMP Form γ water Toluene/DMF Form γToluene/DMA Form γ Toluene/NMP Form γ

Example 9 Process for the Preparation of Polymorphic Form γ ofPerindopril (L)-Arginine

5 g of Perindopril free acid was dissolved in appropriate solvents (10ml) at room temperature and solution of (L)-Arginine (2.3 g) in water (6ml) was added to it and stirred for 2 hours. The results obtained arerepresented in Table 5

TABLE 5 Solvents Volume ratio Result Acetone/water 2:1 Form γEthanol/water 2:1 Form γ 1,4 Dioxane/water 2:1 Form γ

Example 10 Process for the Preparation of Polymorphic Form γ ofPerindopril (L)-Arginine

1 g of Perindopril (L)-Arginine salt is suspended in appropriatesolvents at different temperature and stirred for 12 hours to affordform γ of Perindopril (L)-Arginine. The results obtained are displayedin Table 6

TABLE 6 Temp. Input Solvent Volume (° C.) Result Form α ACN 5 25-30 Formγ ACN 5 70-80 Form γ Toluene 5 25-30 Form γ n-heptane 5 25-30 Form αForm γ ACN 10  80 Form v Toluene 10 110 Form γ n-heptane 10 60-80 Form γAmorphous ACN 10 25-30 Form γ

Example 11 Process for the Preparation of Polymorphic Form γ ofPerindopril (L)-Arginine

1 g of Perindopril (L)-Arginine salt is suspended in appropriatesolvents at different temperature and subjected to variouscrystallization techniques to afford Perindopril Arginine form γ. Theresults obtained are displayed in Table 7

TABLE 7 Volume Temp Input Process Solvents ratio (° C.) Result Form γAntisolvent MeOH/EtOAc 1:10 25-30 Form γ MeOH/Acetone 1:10 25-30 Form γ1,4-Dioxane/ 1:10 25-30 Form γ IPE Pyridine/IPE 1:10 25-30 Form γNMP/IPE 1:10 25-30 Form γ Form α Azeotropic Toluene/EtOAc 1:10  80-110Form γ Distillation Toluene/ACN 1:5   80-100 Form γ Amorphous AzeotropicToluene/ACN 2:5   80-100 Form γ Distillation

Example 12 Process for the Preparation of Polymorphic Form γ ofPerindopril (L)-Arginine

10 g of amorphous Perindopril Arginine salt was exposed to humidity(RH>90%) for 3 hrs. The solid isolated is identified as polymorphic formγ of Perindopril (L)-Arginine.

Example 13 Process for the Preparation of Polymorphic Form γ ofPerindopril (L)-Arginine

6 g of amorphous Perindopril Arginine salt was dissolved in toluene (100ml) and stirred for 10 minutes. The reaction mass was thenazeotropically refluxed for 60 minutes. To this solution, acetonitrile(300 ml) was added at reflux temperature and maintained for 60 minutes.The resulting solid was filtered and dried at 50° C. under vacuum. Theproduct obtained was identified as form γ of Perindopril (L)-Arginine.

Example 14 Process for the Preparation of Perindopril Arginine Form α(as Per English Translated Example 1 of WO07099217A1)

1 g of pure Perindopril free acid was dissolved in 4.5 ml of water at 25to 30° C. To this 0.47 g of (L)-Arginine was added and stirred for 10min to get clear solution at 25 to 30° C. To this methylcyclohexane (2.5ml) was added and stirred for 30 minutes at 25 to 30° C. DMSO (13 ml)was added slowly at room temperature. Solid immediately precipitatedout, continue stirring for 30 minutes. The solid was filtered and driedat 50 to 55° C. under vacuum for 12 hours.

Example 15 Process for the Preparation of Perindopril Arginine Form α

5 g of Perindopril free acid was dissolved in 25 ml of water at 25 to30° C. To this (L)-Arginine (2.3 g) was added and stirred for 10 minutesto get clear solution at 25 to 30° C. The reaction mass was cooled to 15to 20° C. To this cold solution mixture of 12 ml of cyclohexane and 75ml of dimethylacetamide were added slowly at 15 to 20° C. Solidimmediately precipitated out, continue stirring for 1 hour at 15 to 20°C. The solid is filtered and washed with 5 ml of cyclohexane. The wetsolid was dried at 50 to 55° C. under vacuum for 12 hours.

We claim:
 1. Polymorphic form γ of Perindopril (L)-Arginine having a powder X-ray diffraction pattern with peaks at about 4.21, 7.87, 13.19, 14.12, 17.60 20.15±0.2 degrees 2-theta.
 2. A process for the preparation of polymorphic form γ of Perindopril (L)-Arginine according to claim 1 comprising the steps of: a) dissolving Perindopril free acid in mixture of solvents, b) adding solution of (L)-Arginine in water and c) isolating polymorphic form γ of Perindopril (L)-Arginine.
 3. The process according to claim 1, wherein the mixture of solvents is water in combination with an organic solvent selected from ketones, alcohols, and 1,4-dioxane. 